Week 4 ends

Windows finally ordered on Wednesday. I managed to get the window spec selectively trimmed using PHPP to test what effect this would have on the building's performance. The PHPP paid for itself many times over just in this one week of 'optimising' the spec.

Getting to grips with Therm (also after a long struggle). The model of the external floor-wall junction I created, has produced a provisional psi value of 0.15W/mK, lower than the 0.2W/mK estimate I had previously. Putting that more accurate figure has trimmed another 0.5kWh/m2.a off our Annual Heat Demand. Helpful, as it allowed me to trim a bit more off the window spec.

I have a sense of having achieved quite a bit this week.

Meanwhile, the scaffolders have been busy by this time next week, the whole house will be shrouded in a tarp and tin weather shield that will protect the existing structure from the rain and provide a working environment for the site operatives more conducive to accurate and quality work. It also much reduces the risk of weather-related project delays. We have been lucky in that we have missed most of the bad weather affecting the rest of the country, although night time temps have dropped to as low as -10C. Even though we have not had much snow, it has not been nice weather to be working outdoors.

Week 4 begins ... the latest on windows and on thermal bridges

Windows

Week 4 starts and we Still Haven't Placed Our Window Order. The process of placing the order is taking a lot longer than I'd anticipated. I am optimistic that we will be in a position tomorrow, finally, to press the Go button.

This has all come as surprise to me, as I'd thought naively that we could spend time fine tuning our window spec, then present our carefully worked out window schedule to our helpful, local Internorm distributor who would then be able to process it quickly and simply ... no probs, job done.

I realise now that we should have sat down and gone through our schedule with the distributor and talked prices and options at least two months ago, despite not having planning permission or completely finalised window dimensions at that stage. The order process is slow because, while it is easy to spec out the windows for their required energy performance, there are so many other variables to consider and requirements to fulfil. One is the thickness of each pane of glass. If the glazed unit is over a certain area, 4mm glass has to become 6mm. For a given width of bead, this means 4mm less space between the panes, which has a significant impact on the U-value of the glazing. None of these are problems in themselves but overcoming them adds to the cost of the windows unnecessarily.

Better to use slightly less exacting window performance figures in the PHPP. That way, you can order standard products and get a much more cost effective solution. It seems obvious to me now that I am writing this and, in fact, I have used been using conservative figures throughout the PHPP but I think I got carried away by all the exciting "Leading Edge" or best case figures that the different window manufacturers banded about. Assuming your chosen window provider is in the business of manufacturing windows with near Passivhaus performance, the conversation needs to be about what their standard spec is on those windows. It also needs to be about whether window sizes or other variables will make it harder to achieve the energy performance you are planning for in the PHPP.

Here are my rules of thumb:

	My "Leading Edge" Spec Assumptions this time	More conservative PHPP assumptions I will use next time
Glazing "g"-value	0.6 or 60%	0.5 or 50%
Glazing U-value	0.5W/m2K	0.6 or even 0.7W/m2K
Frame U-value	0.94W/m2K	0.94W/m2K
Spacer psi-value	0.038W/mK	0.05 or even 0.1W/mK

I got it right with the frame U-value, because I knew that the "leading edge" spec was a lot more expensive than their standard Passivhaus spec.

These figures aren't set in stone and I'm sure that each year what is considered standard "Passivhaus suitable" spec will improve.

Thermal bridging

On Thursday, I attended a one day course on how to use Therm, together with a very helpful Excel spreadsheet developed by Peter Warm, to calculate the psi-values of thermally bridged building junctions.

Therm is not at all intuitive but does have the advantage of being the only free software that can be used to derive a psi value for many types of thermal bridge. Therm can only model in two dimensions and more complex (and very costly) software needed to model certain types of thermal bridge junctions.

I have been grappling with this for some months but am now finally biting the bullet and getting to grips with Therm, so that we can replace the conservative (I hope) thermal bridge psi-values (0.2W/mK) we have used in the PHPP to quantify the additional heat loss through the floor-wall junctions of the existing house: this type of thermal bridge is unavoidable in a refurb but can be designed out in a new build.

Likewise, I want to model the junction between the existing house walls and the window jambs (sides), heads (top) and cills.

Meanwhile, the first insulation is being installed around the base of the walls of the existing building and in the base of the new build side extension.


We had to buy double quantities of the insulation in half thicknesses because, even though the thicker sizes do exist, the suppliers will only sell them in very large quantities, unsuitable for a project of our scale. I asked our builders to stagger them slightly to reduce possible thermal bridging in the inevitable, if tiny, gaps between each piece. So instead of this...

As we got around the corner, we started adding a 50mm overlap, like this...

It means a little bit of extra labour but it is essentially a free way to get the best from the insulation you are using. The images above are of the insulation around the base of the existing building, 2 x 60mm thick, which we are fitting from DPC level down about 400mm.

Installing dual layer of Foam Glas, under the toe of the concrete slab, where the weight of the walls of the new build will bear down - Foam Glas can take much heavier loads than other insulation  - we are also taking the opportunity of staggering the two layers to minimise unnecessary thermal bridging.

Later this week, the scaffolders will be here to start setting up the shroud that will cover the building for the next three months while the external wall insulation, the windows and the new roof are put in place.

More photos from Weeks 2 and 3 - a comment on cavity walls

More photos from the build here. I may add a couple more during this week. The one below (I can't get it to display correctly, sorry) shows the existing cavity wall insulation, which has become saturated due to water penetration from driving rain (we believe).

Exposed cavity

 We are planning to suck out all the existing insulation with a super powerful, industrial vacuum cleaner. Although the cavity will only be providing a small portion of the total insulative value of the new wall, we want to minimise the risk of gaps, which could allow air movement within the wall. It this happened, the U-value would be badly compromised. The replacement insulation (Instabead Graphite K32) has a significantly lower claimed conductivity value (0.033W/mK) than the rockwool (0.045W/mK).

Week 2 of the build - "To refurbish or not to refurbish"

Week two has been quite eventful. The old windows are out and much progress made in digging trenches for the external insulation and preparing the foundation for the new build element to the side of the house.

All (I hope) of the shortcomings of the existing building have now been exposed and this week I have found myself questioning why we are bothering to refurb and not demolishing what is left and starting again. If we had chosen to demolish it, we would have been able to do away with many hours of difficult design work. The problems of thermal bridging between the ground floor concrete slab and the structural walls would have gone away in an instant. We wouldn't be paying tens of thousands in VAT, as VAT can be claimed back for new builds.

Our builder mentioned as an aside that we could have brought in a big machine that, in no time at all, would have crunched up the concrete that makes up so much of the mass of the existing building. We could have sold it for hardcore at £3 or £4 a bag. This is a good point against the pro-refurbishment argument about saving embodied energy, as the energy in the crunched up concrete would still have had a use in the future, if we'd gone down the new build route.

Despite that, I still strongly believe there is tremendous value in what we are doing. Even if the economics in our case is likely to be marginal, there will be many lessons to be learned from this project for us personally and, I hope, for others for whom refurbishment is the only option.


We still haven't placed our window order and I am now getting quite nervous about it. Having spent so much time and effort optimising our spend and the work programme, I can see money being wasted because of the delays in finalising the windows.


During the week a gas leak was discovered and the site was temporarily evacuated until the leak was provisionally patched up. The local gas infrastructure company is coming back early next week to replace all the pipework from the street to the house. The old pipe was completely rusted away and, as soon as it was exposed, began to leak a lot of gas. It amazes me that a house that was built on a green field site 40 years ago could have been connected to the gas grid with pipework that had no chance of lasting. I have to assume that the gas has been slowly seeping through the ground for many years and that our situation is far from uncommon. If that's true, not only have we been building homes that waste energy hugely, the gas grid itself is wasting gas before it even reaches our gas meters.

Week One photos

I've uploaded some photos of this week's activity here.

Removing all the ceilings has underlined what a big task it will be to make airtight all the junctions with the existing ceiling joists on two floors. The plastering will go up around and between the joists with additional work using Pro Clima airtightness products around each joist.

Week 1 of the build

We started on site this week after a rapid exit into temporary accommodation following long awaited granting of planning permission. I was determined that we would not delay the project, before the build had even started, by failing to move out in time. We only just made it though!

The construction team got to work with great alacrity and a building that had been our home three days before very quickly became a building site. All of the wooden stud partition walls are gone, as is all the internal plaster work, which practically came off on its own. Also gone are all the ceilings, all electrical cabling and sockets and all the old kitchen and bathroom fittings. One of the builders found someone to take all of the pine flooring, which he is going to de-nail, re-sand and lay for a small new build in the neighbouring county. Given that it was installed second hand in our house, it will now be getting its third use, which is very satisfying. Still, despite the fact that nearly all the existing structure remains, five or more skips have been filled so far, although the skip company will sort all the contents to separate out any recyclable material.

The attached garage, which is going to be replaced by a single storey new build, is also gone, except for its concrete floor, which goes next week, together with all the windows. Next week also sees the end of the road for the hideous concrete chimney, an original feature I'm told: I really can't imagine what possessed the architect or builder who specified it back in 1970.

It is interesting seeing the building reveal its structure. The quality of the original workmanship is no longer hidden. The 70mm of underfloor screed was removed today to allow us to insulate the floor with the minimum of increase in finished floor height. Unfortunately, the ceiling heights are not especially generous and we could not simply add the insulation on top of the existing screed. The original concrete slab is now exposed everywhere and, as expected, it is very rough and uneven and we will need to find a way to create a level, even base to place the insulation onto. As I think I discussed in an earlier post, the floor was one of the hardest-to-treat elements in the design stage. We were not able to design a floor with a U-value of below 0.15W/m2K, not without spending silly money on very exotic forms of insulation. We have managed to compensate for the relatively poor (>0.25W/m2K) floor U-value but it is still essential we get 70 to 80mm of insulation in there to get the building through Passivhaus Certification.

This week, we have been going through the fiddly process of building up an order for the Internorm windows. We must finalise the order in the next 12 days to avoid risking delaying the project. I had promised myself that we would not cut things so fine with the timing of the window order but this is proving quite hard to achieve. I can see how easy it is to delay progress on a build by taking your eyes off the windows.

One of our windows consists of a large, undivided, fixed, north-facing, triple glazed unit. If there are no other constraints, it is apparently possible to get a U-value for the glazing (Ug) of 0.5W/m2K without using very rare and expensive Krypton gas. Because UK building regulations require 6mm glass for (for inner and outer panes?) in windows of greater than 1300mm height (?), rather than the usual 4mm glass, we lose precious mm of Argon-filled space between the panes. This constraint means that the glazing can only get a Ug of 0.6W/m2K if we stick with Argon. The PHPP will come into its own again when I use it to check whether de-rating this window's glazing to 0.6 will affect the building's overall performance significantly. It is worth doing, as adding Krypton into this one window adds a few hundred pounds (£££) to its price.

It has been interesting as the builder works on further rationalising some of our design choices: balancing materials cost (financially and environmentally) with labour costs and simplifying the execution to minimise the risk of error that could create unintended thermal bridging or air tightness issues. We have managed to simplify a couple of the building junction details. As a client, it adds fantastic value to the project to have that second design iteration. However, it is only working because of the excellent communication and mutual respect between builder and architect. The importance of this team working, "common purpose" if you like, between architect, builder and of course client, has been underlined for me again this week.

The planning saga

These two posts were written before we received planning permission. It would be so tempting to write a rant about the few, mean-spirited people whose intemperate and ill-informed objections made the whole process so stressful and who, by forcing a redesign and delaying the approval process, added thousands to the project's costs. But I won't. Here are two posts written before approval came through.

18 July
Our property is one of a row of three different units running north-south, within an estate with quite a strong, distinctive architectural style. The roof ridge on all three properties runs north-south. In our original design, we had wanted to rotate our roof to create a 35° south facing roof, optimised for solar hot water and photovoltaic panels and minimising shading in our garden (the house sits on the southern edge of the 550m2 site with a garden that wraps around east, north, west). Although it is not in a conservation area or listed, the planners wanted a design that conforms very closely to the shape of one of the neighbouring properties: this has translated into retention of the north-south ridge line. We will now have a 23° east-west facing roof, matching the current pitch. The change means that the 4kWp solar PV array we are planning will generate 500kWh a year less than it would have done: equivalent to 12.5MWh less over 25 years. It is annoying for us, as it means £21 a month less Feed-in-Tariff income but it is also extraordinary that one arm of the state prioritises subjective aesthetics while another is rightly concerned with replacing our ageing fossil fuel based electricity generating capacity with non-fossil fuel based alternatives. Given that we are losing an unprecedented proportion of our existing generating capacity (30+%) over a decade and that a portion of the rest is based on gas, which has significant security of supply issues, you'd think that all public policy would reflect this imperative.

27 September

I write tonight on what I believe and hope to be the eve of a positive decision to approve our revised plans. The planning process has been horrible. We took a big chance by doing so much design work at risk. This being our first Passivhaus project and a refurb, made it very hard for us to do otherwise. The planning system needs urgently to be redesigned to:

• make local decision-making less arbitrary - decisions need to be governed by policy and much less by subjective matters of aesthetics
• for smaller householder scale projects, which according to Wikipedia make up 60% of all planning applications, the public should be restricted to a form online and on paper where objections can only be made based on specific issues: loss of light, privacy or other amenity; or on other issues that relate to the local planning policy. The "any other comments" box should be small! Our application generated a huge number of words that took time and resources to read, analyse and read.
• There needs to be an explicit warning to the public on the comments form that comments or attacks of a personal nature are not acceptable and will count against any point the commenter wishes to make.
• The planning process needs to be integrated with the building control process.
• Conservation issues seem to hold sway over sustainability issues - this imbalance needs to be addressed urgently

28 October

Well, it's now a month later and we have this week finally got our planning permission. I feel relieved but battle weary. It has been very scary having committed so much resource to the project, knowing that I could not be certain that it would actually go ahead.

We hope we have all our ducks in a row now and can get started very soon.

What shape of building works best

At this year's AECB conference two weeks ago, Peter Warm gave an informative talk on the Passivhaus certification process. One of his PowerPoint slides showed the impact of a building's form on the wall U-values needed to get to the 15kWh/m2.a target.

By dividing the total "heat loss" area by the "treated floor area", you get a ratio which describes how compact the building form is. The "heat loss" in most cases is, essentially, the sum of the areas of the building footprint (ground floor), roof and external walls; all measurements taken externally. The "treated floor area" or TFA is the usable internal floor area; calculated according to the convention used in Germany (as you would expect, given that the Passivhaus standard originates there). The higher the form factor ratio, the lower the U-values need to be to reach the target.

Non-compact detached houses, particularly bungalows, score the worst, sometimes with a ratio as high as 5. They need walls with a very low U-value of around 0.05 to get to the 15kWh target. Blocks of flats typically have a ratio of 2 and they only need wall U-values of around 0.15 to reach the Passivhaus target.

Semi-detached and terraces are somewhere in-between.

Form factor ratio	Typical wall U-value
4 < 5	0.05
3 < 4	0.10
2 < 3	0.15

This means that, if you want to build a Passivhaus with reasonably sensibly sized walls (i.e. less than 500mm thick) or using natural materials or at a sensible cost, you really are going to have to pay attention to the shape of your thermal envelope; the building itself can be any shape you want but the "warm" space (contained by the thermal envelope) needs to be compact.

In our project, our form factor ratio is 2.53 - so I'm feeling quite pleased with myself, even though this was partly by luck.

In Passivhaus refurbs I think that building form is as least as important as orientation and solar gain, if not more so.
      
                       

Interesting post on Green Living Blog at Guardian.co.uk

There is a lot of talk about the importance of using low embodied energy materials in construction. In our project, there is an element of new build, as well as the refurbishment of the existing house. As I have noted previously, we found that it was impractical in this project to use natural, low embodied materials exclusively. In particular, constraints of the existing structure have meant that we are using a lot of Phenolic foam to insulate the floor (on top of the concrete slab) and externally on the walls. In the new build element we are mainly using wood-based structural and insulative materials.

There is an interesting post on the Guardian's Green Living Blog about this. In a study in Scotland, a two bedroomed cottage takes 80 tonnes of CO2e to build, using standard building techniques and materials. If built to building regs energy efficiency levels, this is the equivalent of six years' energy consumption/CO2e emissions living in the cottage. If that cottage were a Passivhaus, and assuming the energy needed to build it was similar to the standard build, it would take 60 years to 'payback' the energy/CO2e. This gives some support to the argument used by natural material proponents that, if you build a very low energy house, the embodied energy in construction becomes proportionately more important in determining the building's lifetime energy consumption. In the post, they have concluded that refurbishing is the best option (compared with either new build or do nothing) because a refurb of the same sized property is only emits 8 tonnes of CO2e.

Here is a quote from the article. The link to the original is here.

"80 tonnes is a lot – equivalent to five brand-new family cars, about six years of living for the average Brit or 24 economy-class trips to Hong Kong from London. But a house may last for a century or more, so the annual carbon cost is much less – and for all the new-build options, the up-front emissions from construction work were paid back by savings from better energy efficiency in 15–20 years.
However, the winning option was to refurbish the old house, because the carbon investment of doing this was just 8 tonnes CO2e, and even the highest-specification newbuild could not catch up this advantage over the 100-year period. Once cost was taken into account, refurbishment became dramatically the most practical and attractive option, too."

Project Update - September 2010

We are still awaiting a decision from the planners, although lots of work continues in the interim, there's nothing Passivhaus specific to report on this month. Watch this space...

New Passivhaus Refurb Standard announced

The Passivhaus Institute is finally to announce a long trailed standard for refurbishments. This new standard, to be known as EnerPHit, will be easier to achieve. The headline targets are:

25kWh/m2.a - annual heat demand
1.0 - air changes per hour - airtightness standard

There'll be more detail on what assumptions lie behind these standards in the coming weeks I hope. Refurbishments to near Passivhaus standard will now be recognised with this new standard. The less stringent standard will make Passivhaus thinking and methodology more accessible to those refurbishing by giving them a challenging but achievable standard to aim for. I imagine that the procedure to gain EnerPHit certification will be similar to that for the full Passivhaus standard. Certification adds value by enforcing a certain discipline to the design and build process. This benefit will now to open to the refurb sector.

We will still be sticking with the full Passivhaus standard for our refurb. Being based in the south west of England has made it feasible to aim for. If our project had been located in Manchester, the colder climate there would make the full Passivhaus standard unrealistic practically and financially for us. The new EnerPHit standard would be within reach though.

Before we all relax too much, a quick comparison with other UK building standards reminds us that this new PH refurb standard is still far ahead of others; it will still be a huge challenge to get EnerPHit certification.

PHPP and planning

We are still in planning, having revised our design in July to reflect the planners' concerns. The new design is currently out to 21 days' consultation (ending 25 August). The change meant we had to go through most of the data we had entered into the PHPP, as well as re-visiting some of the airtightness and thermal bridge detailing, to make sure that we could still meet the Passivhaus standard.

During that process, I discovered I'd made a silly but easy-to-make error in how I had entered data into the PHPP. I hadn't assigned all the areas I had defined to the correct building elements. Luckily, this error was in our favour. After I'd corrected the PHPP, our annual heat load figure dropped considerably so that we should be within the 15kWh/m2.a without having to include any particularly expensive options. It has taught me a lesson about how to minimise the risk of a similar mistake in future. It really is worth calculating the treated floor area separately and entering the total figure into the PHPP. It makes it easier to spot errors of the type I made.

I hope that we will have some good news about the planning soon, so that we can start on the build as soon as possible. Watch this space!

Joyous buildings

Recently, I had the opportunity to meet Richard Hawkes, whose very attractive house Crossways appeared on an episode of Grand Designs last year. His project has just gained Passivhaus certification, which is great. Congratulations!

When I met Richard and on his blog, he expressed his belief that the PHPP is a block to creating "joyous" buildings and, now that he has certification, that the PHPP is redundant. Indeed, the PHPP seems to be generally a Bad Thing; as well as interfering in the creative process, it is antithetical to collaborative working.

I am amazed that the PHPP, which is after all just an Excel spreadsheet, albeit a very sophisticated one, has such power over architects, builders and others working in the built environment that it can prevent them from producing beautiful designs or working collaboratively. My experience as the client and Passivhaus designer during the design phase of our project does not bear this out. We have found the PHPP to be a very useful tool in helping us to optimise our design, for instance by not over spending on unnecessary insulation or by focussing our attention on detailing critical areas correctly. However, the PHPP does not design the building for you. It is still up to the architect to use their creativity and experience to deliver a building that uplifts, that is "joyous". It is still essential to work collaboratively on the project, indeed collaborative working between client, architect and the builder (who should be identified and involved early in the project) is probably the most important success criterion in a Passivhaus project. The PHPP is merely one of the tools in the design tool-kit.

We have been more constrained by other factors, primarily by the fact we are refurbishing an existing property, rather than building from scratch. Also, our house is on an estate with a strong architectural character and it is this, other site constraints, financial constraints and the requirements of the planners that are driving our design, not the PHPP!

I think that Richard is right when he talks about experience. The Passivhaus design process uses a lot of rules of thumb, derived from many years' collective experience, to get the initial design broadly correct; this is something that an experienced, certified Passivhaus Designer can bring to a project. Having produced an initial draft of the plans informed by those rules of thumb, the PHPP is there to help to highlight potential problems in the design. It is still up to the architect, Passivhaus Designer, client and builder if they want to aim to use the PHPP to achieve Passivhaus certification. They may decide that a particular aspect of the design is more important than reaching the full certified Passivhaus standard. Using the PHPP properly means this decision is a concious one, rather than an unintended error. In that scenario, the PHPP can sometimes help identify other areas where the shortfall can be made up elsewhere in the design. In a world where Passivhaus design is the norm and understanding of Passivhaus design and methodology has been widespread for decades and is embodied in the DNA of all the professions working in the build environment, the PHPP would probably become considerably less useful. However, particularly here in the UK, where we are very far from this, the PHPP will remain a useful tool for a long time.

I would add that in a refurb, where nearly every project needs a bespoke design, the need for the PHPP is even greater. In a new build, provided that client, architect and builder have that "Passivhaus DNA", whether or not they would recognise it as that, and particularly in the less challenging (meteorological) climate of southern England, Richard Hawkes has shown that it is possible to reach certification. However, I wonder whether he could not have trimmed some elements of his design* and saved himself a bit of money by using the PHPP tool earlier on.

* I am referring to those relevant to the building's energy performance, not those that make it "joyous"

[edit 27 Jul] This recent article on the Centre for Alternative Technology's new WISE building continues the debate.

Windows revisited

We have made a few changes to the windows.

We decided to use Internorm some months back for various reasons discussed in a previous post. We had planned to use their "Varion" triple glazed range in the north and south windows and Varion 4 range - with triple glazing and a fourth pane that encloses integral, external blinds - in the east and west windows, of which we have too many; this is to compensate for constraints on the south side of the site. An ideal Passivhaus has lots of south facing windows - ca. 25% of the south façade area; modest amounts on east and west façades and minimal window area on the north façade. There's more on our east west windows and the Varion 4 dilemma further down this post. First, something about skylights...

Internorm do not make skylight windows and so we looked at Velux and Fakro, who do. We had planned a large Velux window that the top of the south facing side of the roof. But this window has now been ditched. It would have added more light in our stairwell but we are already improving the daylighting dramatically, so the extra provided by the Velux didn't seem essential. We had also thought it would provide nice stack-effect cooling in summer, being at the top of the house. We (I) have been put off by Velux's poor communication, their incomplete technical data and by a lack of confidence that we would be able to detail and execute the installation well enough. In the PHPP, a Velux would only have brought a net benefit in winter solar gain if the window spec and installation had been good enough. Putting in conservative estimates into the PHPP (in lieu of verifiable data) for the Velux window/installation resulted in no net benefit in heat gain from the window - the additional losses resulting from installing the Velux roughly balanced the solar gains through the window. The window we were looking at was one aimed at the Passivhaus market, although they don't market it in the UK. Trying to get the key information needed for the PHPP from window manufacturers seems to be quite hard. The U-values for the frame and the psi-values (the linear equivalent of U-values) for the spacers (the bits that hold the panes apart around the edge of the sealed double/triple glazed units) seem always to have eluded us! These two factors have a significant impact on the whole window's performance and tend to be the poorest performing parts of a window. Also, it wasn't clear whether the window had a single or a double, all round gasket - the latter being essential for reliable, durable airtightness in an openable window or door. Velux's figure for the "g-value" of the triple glazed unit was not great either, 0.46, meaning that only 46% of the sun's heat energy is let through the glass. 0.50 is the minimum for a Passivhaus; 0.60 or higher is worth aiming for.

The other manufacturer that makes a triple glazed skylight-style window is Fakro. I didn't investigate their products in as much detail as the Velux because, by that stage, the whole idea of a skylight in our project was beginning to look less appealing. The other issue with a south facing skylight high up in a stairwell is that you need an electrically powered and electronically controlled mechanism to open and close the window and its external shuttering. Without these, the window would be a source of summer over-heating. With them comes over complexity and problems if (when?) the mechanism fails.


Back to the east west windows. On a visit to Internorm's shiny new showroom last week, we learned that the only way we could get Varion 4 triple glazed with a fourth pane for integral, external blinds, was to use krypton gas, instead of much cheaper, more abundant but less highly performing argon to fill the sealed units; this is due to space constraints. You can make krypton units much slimmer for the same performance and their main market is in listed buildings, where a high performance double glazed unit can be designed to look like a traditional single glazed window. The external blinds are important to keep overheating well below the modest Passivhaus target of less than 10% of days annually where internal temperatures rise above 25C. If we had been able to have less east-west glazing, we could have managed with the standard Varion windows and more ad hoc shading arrangements. The other problem with a total of four panes, is that our g-value for the window would have been less favourable than with the standard triple glazed Varion windows.

It is possible to fit shutters or non-integral external blinds but using these created other difficulties because of other constraints arising from this being a refurb project.

So now, we have decided to go for the double glazed Varion 4 windows with a third pane to enclose the integral blinds for most of the east west windows. It seems that, although they are not true triple glazed units, the third pane provides a measure of additional insulation, a bit like secondary glazing can do, with the U-value coming in at around 0.9 to 0.95.

Putting these windows into the PHPP did have a small effect on the annual heat load. The last concern was about the temperature on the interior surface of the window. One of the key principles of Passivhaus design is to ensure that no interior surface has a temperature more than 4C lower than the ambient temperature - a bigger temperature gradient reduces thermal comfort and risks creating draughts. Using a U-value of 0.95 and a worst case scenario of a winter night of -10C gives you a temperature of 16.3C in the calculation below, still just warm enough.
In practice, I am sure that these windows will be fine and even though they appear to be ok, just, Passivhaus wise, I suspect that it may make certification more problematic. Watch this space!

p.s. Have just realised that it is possible to insert pictures anywhere in the text and to insert more than one per post, so will definitely use more in future.

Passivhaus and the planning system

Well, our plans are currently in planning and we are living in limbo, uncertain whether the months of work we have put into the design and the PHPP calculations will translate into the home of our dreams.

The UK planning system does not fit well with the Passivhaus approach, which involves much more upfront, detailed design work than a traditional build. Normally, an architect produces an outline design with just enough detail to satisfy the planners; the point being not to commit more resources than necessary until after planning permission has been given. In any Passivhaus project, but particularly in ours, which is much more challenging because we are new to Passivhaus in the UK and because it is a refurb, more work is needed to be sure we would meet the Passivhaus standard before the planning application can be submitted. If we had submitted our plans earlier, we would have locked in window sizes and other variables that have a significant bearing on the building's energy performance. We have found getting down to the key Passivhaus standard for heating of 15kWh/m2 per annum quite difficult, without throwing silly money at some exotic materials.

Similarly, although we are stuck with some thermal bridging - at the floor wall junction of the existing house - we have managed to eliminate most other potential bridges. If we had submitted our planning application earlier, we would almost certainly have inadvertently designed in thermal bridges into other junctions.

All this means that we have had no choice but to stick our necks out and spend a lot more before planning permission has been secured. The alternative would have been probable failure to achieve the Passivhaus standard and unnecessary design work and building costs later in the project.

As a newcomer to the construction sector, it strikes me that more detailed design work, early on, pays dividends. The build costs should be easier to tie down accurately before contracts are signed and the build starts and there should be much less risk of unexpected costs. Of course, being a refurb, there are still some unknowns which could throw a spanner into the builder's cost estimates. By the time we submitted our plans, we were only a week or two away from being ready to submit plans to building control.

Maybe, in these times of looming public expenditure cuts, it would make sense to combine the full planning application and building control application into a single approval process, with a much simpler initial approval in principle procedure for new builds and larger schemes or where a building is listed or in a conservation area. Whatever the solution, the planning system needs to give clients and architects enough certainty about a project early on to allow them to commit the resources necessary to do the more detailed design work required for a Passivhaus.

April update

We have spent the last month continuing to tweak and refine the design. It seems to be what we were doing last time I posted but the process is iterative and a few days ago we got to the point where we felt we could submit our planning application. Window placing and sizing, both hard to change after planning, have a big effect on the performance of a Passivhaus, so we had to be sure this was right before submitting planning.

Next, we are working out where all the ductwork for the heat recovery ventilation (MVHR) will go. The MVHR is a small unit, typically a metre and a bit square by half a metre. It needs to be located very near an external wall for maximum energy efficiency and, although barely audible, away from bedrooms and living areas. In our refurb, it will be going into the loft. The principle of MVHR is to extract stale air from kitchens, bathrooms and WCs through extraction ducts back to the MVHR unit where it passes through the incoming air whilst remaining physically separate. In this way, most of the heat (at least 75% in a Passivhaus) is transferred to the fresh incoming air. This new air then supplies the living areas and bedrooms through a separate network of supply ducts. Air is moved very slowly through large, smooth sided ducts, with silencers between rooms to eliminate perceptible noise. Choosing a good MVHR unit, designing the ducts and the room valves, and configuring the whole system once installed are vital parts of achieving a Passivhaus. The MVHR ensures that the internal air is always fresh, even when the windows are closed during the heating season. It means that the building is continually being aired - something we normally have to do briefly as a daily ritual. It gives a much better indoor air quality than virtually all other modern and many older buildings without sacrificing the building's energy efficiency.

The other great thing about using MVHR in a Passivhaus is that you can use it to distribute heat around the house; but only if your building needs very little heat. The air can only carry a very small amount of heat because the air moves through the ducts quite slowly (to avoid wasting energy or creating air noise by running the fans at a higher speed) and because the air can only be heated to about 30C above room temperature. These physical constraints translate (once you do the physics) into a maximum of 10W/m2 maximum heat load that can be conveyed by the ventilation system. For a typical UK home of around 100m2, 10W/m2 translates to 1000W (or 1kW). Compare this with the output of many UK gas boilers: 25kW or more. If your building can be heated with such a small heat input, you can use the MVHR as your heating system as well as your fresh air system, saving upfront capital costs and reducing on-going maintenance. In fact, an MVHR is a very simple system, not to be confused with heat pump systems or air conditioning systems. The only regular attention it needs is a change of air filters, something you can do yourself - there's no need for any servicing. The units use very little energy, many times less than they save.

Floor wall thermal bridge, the plot thickens
We have revisited the floor-wall thermal bridge problem. In a new build it is possible to design out thermal bridges but in our refurb, there is no economic way to do so. When you get a building as energy efficient as a Passivhaus, any remaining weaknesses, such as thermal bridges, can become quite significant sources of heat losses. In the PHPP, it is possible to include figures for the thermal bridge losses, however the calculations you need to get the figures are complicated. One good reason to design them out if you can.

This time I used another free, if infuriating, piece of software called Therm, which is intended for window designers but which can be adapted for other purposes. It allowed me to calculate a "U-factor" (as distinct from a U-value) for the external floor-wall junction, something which Heat 2, which I mentioned in an earlier post, doesn't do.

Once you have successfully calculated your "U-factor" in Therm, a further manual calculation is needed to gives you a psi-value for the junction: the psi-value is the linear equivalent of the U-value. Multiplying the psi-value by the length of the junction gives you the number of Watts the junction will lose for each degree centigrade difference between inside and outside.

The convention in Passivhaus is to use the U-value and the external dimensions to calculate heat losses through a wall or other area, rather than the internal dimensions normally used here in the UK. The Passivhaus convention of using external dimensions means that, at corners, the area is double counted, resulting in a slightly over conservative figure for the building's overall heat loss. In a well designed new build Passivhaus, this allows for any minimal thermal bridging that might remain. In our refurb, the thermal bridge looks like it will be significant and I don't know yet whether it will stop us achieving the Passivhaus standard. The Passivhaus Institute are planning to relax the standard for refurbishments because in part, I suspect, of the extra heat loss caused by these unavoidable thermal bridges.

External insulation
We have managed to reduce the thickness of the external from 300mm to 180mm. Originally, I'd hoped to use an insulator made from a tongue-and-groove wood fibre board product, like Pavatherm. The insulation would have had to be more than 300mm thick to achieve a wall U-value of 0.1. As this would have been applied to an existing wall of 300mm, the external walls would have been excessively thick. The weight of the insulation would probably have posed structural issues too, possibly requiring reinforcement of the footings. Instead, we are using Phenolic foam, which will deliver the same performance for half the thickness as wood fibre. Even though Phenolic foam is made from fossil fuels and has a higher embodied energy, our solution is overall less energy intensive than the wood fibre alternative. At 180mm, Phenolic foam costs £40/m2 or £100/m2 including installation, so not cheap. However, the thickness of the insulation has turned out to be more than just an aesthetic matter. The deeper the insulation, the deeper the windows are inset into the walls. This cuts down the amount of solar energy the windows can capture and negates some of the additional benefit of the thicker insulation.

Part of our refurb is a new build extension. Here we are using wooden I-beams in-filled with a cellulose insulation like Warmcel. I-beams are so called because they have the shape of a capital letter I when looked at end on. This design, using engineered wood, gives high strength with less thermal bridging because of the thinner central section. We will also be using I-beams in-filled with cellulose in the roof. An I-beam construction can become a source of thermal bridging unless the wall is carefully designed so that the "I" of the beam does not run through the entire thickness of the wall.

As all Passivhaus projects have to manage thermal bridging between and within walls, floors and roofs, a very helpful group of people have produced a compendium of building drawing and materials details that architects and Passivhaus Designers can copy, rather than always trying to re-invent the wheel. The "Passivhaus Bauteilkatalog" is in English and German. It costs about £81, so not cheap, but cheaper than doing all the work yourself.

A lot has happened since the last post. I have been working on the Passive House Planning Package (PHPP), the very sophisticated Excel based spreadsheet used to model how your proposed building will perform. I had spent a lot of time getting to grips with the basics of entering our proposed building's parameters - areas, materials, glazing, window frames; together with the climate and any shading - which is a bit tedious but which has to be done accurately if you want the PHPP to predict how the real life building will perform. It was only when I started getting initial estimates of how the building would consume, especially whether we were going to make it down to the magic 15kWh/m2/annum, that the power and usefulness of the PHPP really became apparent. Since then, I have been refining the information going into the PHPP and it has allowed us to pinpoint the problem areas and tweak the design further to optimise performance. The floor is still our biggest obstacle. It definitely does not not make sense to remove the slab, as this would also mean removing all the internal supporting walls, all of which we would otherwise want to keep. My earlier modelling of the floor-wall junction may have been too optimistic, as I had only assumed a temperature of zero outside, when -10C would be a more realistic worst case. Also, the outside walls will likely perform better, as they will have insulation outside, right down to the footings. The inside walls won't have this insulation and are therefore probably a bigger thermal bridge. We have added south facing glazing in the roof, following a visit to Ecobuild earlier in the month. Velux now do a triple glazed window with an overall U-value of 0.82. The window has an integrated external blind (essential in a south facing roof window) with remote controlled operation - even though I am not keen on excessive complexity and gadgetry built into the fabric of the house, when the window is 4m or 5m up, I'm willing to make an exception. I had wanted to avoid using roof windows, as I think it is very hard to avoid thermal bridging around the frame. How a window is installed makes a huge difference to its performance. Even with good double glazing, the way it is installed can boost or degrade its rated performance a lot. In a Passivhaus, as well as avoiding thermal bridging, the window has to be fitted to create an air-tight seal around the frame and set in the wall so that the wall reveals and overhang do not create additional shadowing on the window. In a standard block or brick built house, this means wrapping the external insulation around the window frame on the outside so that the window frames will look quite slim from the outside. Also, the rough opening, into which the window is to be installed, needs to be plastered accurately and smoothly, and let to dry out fully, before the window is installed. This allows the specialist tapes, used to make the building airtight, to be fixed between the window frame and the plasterwork to form a good air-tight seal. This changed sequencing of work is quite different to conventional builds but is essential in a Passivhaus. These tapes should be used around the frame, even when air-tight bands are placed between the frame and rough opening. Such bands are designed to expand once in place, so making a good seal but the tape provides a second layer of airtightness and it is easier to patch it if the building fails it's airtightness testing during the build (more of this later). Visiting Ecobuild, it was possible to compare triple glazed windows. Many only have a single rubber gasket to maintain the airtight seal between the opening section and the frame. Although it may perform adequately when the Passivhaus is first commissioned, it is likely to fail over time. Better designs have double or treble gaskets and use engineered wood, which does not warp nearly as easily as its non-engineered counterpart. On airtightness testing, we will need to test at two points during the build: after the windows go in but before the 'first fix' and again after first fix. This is essential because there is not much point in identifying any failures in the building's airtightness after it is all finished. It is much easier and cheaper to resolve problems before all the finished surfaces and fittings are put in. On a wider note, new passive houses are between to get formal certification from the Passivhaus Institute. One of the latest was a house in Kent featured on Grand Designs. Congratulations to them! We will kick off the process for getting certification after we have got through planning. We want to get our planning application off this week. In a conventional build, we could have sent our application off some time ago but in a Passivhaus this is much more risky as we had to do a lot more detailed design work, aided by the PHPP, to get the building working right first, before we could apply for planning permission. Otherwise we might have found ourselves unable to change something that is crucial to the building's energy performance. This might be a real barrier for some people, as it means spending more on architect's fees while the project is still not certain to go ahead.

January update

I have not written anything on the blog for few weeks now. This has not been due to lack of activity!

We are working on the design. I don't see it as a problem that we are taking plenty of time to get the design right. It is much cheaper to change things at this early stage! The architect pointed out another thermal bridge problem that I'd failed to notice before. Part of the building, currently a garage, is attached to the neighbouring house. We need to re-look at our solution to eliminate a significant thermal bridge at the corner with the neighbour. I also want to minimise any party wall issues if possible, as I've never met the owner; he lives 12,000 miles away.

I am also starting to enter data into the PHPP - Passivhaus Planning Package - the huge Excel-spreadsheet based tool used to model proposed Passivhaus developments. The data entered, and any assumptions made, all need to checked very carefully. It is very easy to overlook something that will give you an over optimistic picture of how the house will perform. It is vital to use the tool during the design phase, as correcting problems that it flags up, like the potential thermal bridge I missed above, is often very difficult and expensive.

We have chosen our favoured window provider. Unfortunately, there are no manufacturers of Passivhaus Institute accredited windows in the UK. Until the Passivhaus market grows, this is unlikely to change. Using windows with the PHI accreditation is important because it means that technical performance of the windows has been independently scrutinised and tested. It gives confidence to Passivhaus builders that the windows will do what they say they do on the tin.

[Edit on 23/Jan/10 - there does appear to be one UK manufacturer, Greenspec, who produce a range known as "ecopassiv", that claims a whole window U-value of 0.75, which would be low enough to meet the Passivhaus standard. They do not appear to have certification from the Passivhaus Institute but do meet the AECB Carbonlite Gold Standard. There is more information here: http://www.greenspec.co.uk/html/product-pages/ecocladwindow.php - click on the product brochure for the ecopassiv range.]

Because we are forced by the constraints of the existing building to have quite a lot of east and west facing glazing - not ideal because unshaded east/west windows cause summertime overheating - we wanted a window with integrated external Venetian blinds. This will allow us to keep the daytime heat out without plunging the room into darkness. I also much prefer "tilt-and-turn" windows that open inwards and can be operated with one hand. They are so practical in many ways; once you have lived with them, any other type of window seems unsatisfactory.

The other vital task now is choosing our builder and deciding how we are going to work. A very formal arrangement of tendering, backed up by copious documentation, will not give us the flexibility and the type of working relationships we need. It is very easy to get focussed on the hardware of a Passivhaus, and on modelling it in the PHPP, but one of the most important decisions in the project is choosing your two key partners - the architect and the builder - building a trio that co-operates well as a team. This is, of course, very important in all builds but especially so in a Passivhaus where there is very little room for winging-it with last-minute workarounds to correct mistakes. In Britain I think we are great at winging it and less good at following a proscribed methodology. I am no exception to this. And both approaches have their pros and cons of course. The other vital ingredient is very good communication between the trio of client, architect and builder, with all of us checking that the others have the same understanding of how to proceed. It also means all parties have to be be engaged, really to want to achieve the Passivhaus standard. I'll write more about this later I'm sure.